AU2001266186B2

AU2001266186B2 - Composite centraliser

Info

Publication number: AU2001266186B2
Application number: AU2001266186A
Authority: AU
Inventors: Thomas John Oliver Thornton
Original assignee: Tercel IP Ltd
Current assignee: Tercel IP Ltd
Priority date: 2000-06-30
Filing date: 2001-06-28
Publication date: 2006-08-24
Anticipated expiration: 2021-06-28
Also published as: DK1295008T3; GB0230130D0; GB2381815B; DE60141139D1; ATE455932T1; AU6618601A; US20080156488A1; US7357178B2; WO2002002904A1; EP1295008A1; GB0016145D0; EP1295008B1; US7604059B2; US20030164236A1; WO2002002904A8; GB2381815A

Abstract

An improved centralizer is provided for centralization of tubulars such as casings, liners, production tubing, and production screens, in oil/gas wells. Such a centralizer comprises a tubular body, wherein a portion of an outermost surface of the tubular body is formed from a first material, and a portion of, or portion adjacent to, at least one end of the tubular body, and/or a portion of an innermost surface of the tubular body, is formed from at least one second material, in contrast to unitary construction centralizers disclosed by the prior art, and the first material has a lower Young's modulus than the at least one second material.

Description

1 ND COMPOSITE CENTRALISER

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FIELD OF INVENTION This invention relates to downhole tools; particularly, though not exclusively, the invention relates to an improved centraliser for centralisation of tubulars ND such as casings, liners, production tubing, production 00 screens and the like, in oil/gas wells.

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BACKGROUND TO INVENTION As a borehole is drilled it is necessary to secure the borehole walls to prevent collapsing and to provide a mechanical barrier to wellbore fluid ingress and drilling fluid egress. This is achieved by cementing in casings.

Casings are tubular sections positioned in the borehole, and the annular space between the outer surface of the casing and the borehole wall is conventionally filled with a cement slurry.

After the well has been drilled to its final depth it is necessary to secure a final borehole section. This is performed by either leaving the final borehole section open (termed an open hole completion), or by lining the final borehole section with a tubular such as a liner (hung off the previous casing) or casing (extending to the surface), whereby the annular space between the liner or casing and the borehole is filled with a cement slurry (termed a cased hole completion).

The production tubing is then run into the lined hole and is secured at the bottom of the well with a sealing device termed a "packer" that seals the annulus so formed between this production tubing and the outer casing or liner. At the top of the well the production tubing is fixed to a wellhead/christmas tree combination. This production tubing is used to evacuate the hydrocarbon.

PI1611AU NO In some instances instead of running a final liner string, the final borehole section is left open and screens are run. Screens are typically perforated production tubing having either slits or holes. These screens once in position act as a conduit in a procedure to fill the annular void between the borehole wall and the screen by O placing sand around the screen. The sand acts as a filter 00 and as a support to the borehole wall. The term used for

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NO this operation is "gravel packing" In each case centralising a tubular within a borehole or within another tubular is necessary to ensure tubulars do not strike or stick against the borehole wall or wall of the other tubular, and that a substantially exact matching of consecutive tubulars positioned in the borehole is achieved, while allowing for an even distribution of materials, i.e. cement or sand, placed within the annulus formed.

Centralisers for drill-strings used to aid in the directing of a drill bit within a borehole are documented.

More recently casing centralisers have been described which aim to keep the casing away from the borehole wall and/or aid the distribution of cement slurry in the annulus between the outer surface of the casing and the borehole wall. Examples of casing centralisers are disclosed in the following: US 5,085,981 (MIKOLAJCZYK) discloses a casing centraliser comprising a circumferentially continuous tubular metal body adapted to fit closely about a joint of casing, and a plurality of solid metal blades fixed to the body and extending parallel to the axis of the body along the outer diameter of the body in generally equally spaced apart relation, each blade having opposite ends which are tapered outwardly toward one another and a relatively wide outer surface for bearing against the well-bore or an outer P11611AU ND casing in which the casing is disposed, including screws extending threadedly through holes in at least certain of the blades and the body for gripping the casing so as to hold the centraliser in place.

EP 0 671 546 Al (DOWNHOLE PRODUCTS) discloses a casing centraliser comprising an annular body, a substantially IND cylindrical bore extending longitudinally through said 00 body, and a peripheral array of a plurality of

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ND longitudinally extending blades circumferentially distributed around said body to define a flow path between each circumferentially adjacent pair of said blades, each said flow path providing a fluid flow path between longitudinally opposite ends of said centraliser, each said blade having a radial outer edge providing a well-bore contacting surface, and said cylindrical bore through said body being a clearance fit around casing intended to be centralised by said casing centraliser, the centraliser being manufactured wholly from a material which comprises zinc or a zinc alloy.

WO 98/37302 (DOWNHOLE PRODUCTS) discloses a casing centraliser assembly comprising a length of tubular casing and a centraliser of unitary construction (that is, made in one piece of a single material and without any reinforcement means) disposed on an outer surface of the casing, the centraliser having an annular body, and a substantially cylindrical bore extending longitudinally through the body, the bore being a clearance fit around the length of the tubular casing, characterised in that the centraliser comprises a plastic, elastomeric and/or rubber material.

WO 99/25949 to the present applicant also discloses an improved casing centraliser.

The content of the above-mentioned prior art documents are incorporated herein by reference.

P11611AU 1 IND As is apparent from the art, many centralisers have been developed to overcome known problems of centralising a tubular and distributing an annulus material. These centralisers are of unitary assembly and are made of a 5 plastic, or more generally, a material such as zinc, steel or aluminium. However, in selecting a single material a IND trade-off must be made as: 00 the chosen material must provide a low friction

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ND surface against the smooth tubular outermost surface 1 0 while being strong enough to withstand abrasion from Srugeous borehole walls; the chosen material must act as a journal bearing once the centraliser is in its downhole location, but during the running operation it must act as a thrust bearing.

Material such as plastic deforms, and may potentially ride over stop rings or casing collars. This may occur when the centraliser contacts ledges (possibly the ledges within the BOP stack cavities and wellhead) when run in a cased hole, or to ledges and rugous boreholes when run in open hole. The centraliser is driven along the tubular in the opposite axial direction to that of the tubular motion and is driven into the rings and/or collars.

Additionally, when the tubular is rotated (a common procedure when running tubular downhole, converting drag friction to torque friction) the "nose" of the centraliser is forced against a stop-collar and the tubular rotated thus causing the centraliser nose to act as a thrust bearing. If the centraliser deforms and rides over the collar, the stretched material may jam the centraliser, and possibly the tool or assembly against the borehole wall. This is illustrated in cross-section in Figure 1, where centraliser 110 lies between tubular 140 being centralised within borehole 152. Centraliser 110 of P11611AU ND centralising apparatus 140 has been caused to stretch over stop collar 144 and as a result jammed outermost surface 112 of centraliser 110 against borehole wall 152.

It is an object of at least one embodiment of the S 5 present invention to obviate or at least mitigate at least one of the aforementioned disadvantages.

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00 SUMMARY OF INVENTION

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ND According to a first aspect of the present invention there is provided a downhole centraliser comprising a Scasing, liner or screen centraliser or a production tubing centraliser, the downhole centraliser being adapted to be received on a downhole tubular, in use, so as to be a clearance fit around the downhole tubular such that the downhole centraliser is rotationally and longitudinally moveable relative to the downhole tubular, the downhole centraliser being a rigid tubular body, the tubular body having a first portion and at least one second portion, the first portion and the at least one second portion being statically retained relative to one another, the first portion comprising a tubular member providing an outermost surface of the tubular body, the first portion being substantially formed from a first material, and the at least one second portion comprising a ring member provided at or adjacent to one end of the tubular member, the at least one second portion being substantially formed from a second material, the first material having a lower Youngs modulus than the second material, and wherein the first material substantially comprises a thermoplastic polymer.

The at least one second portion may comprise a further ring member provided at or adjacent to another end of the tubular member. At least a portion of an innermost P11611AU ND surface of the tubular body may be provided by the ring member and optional further ring member.

According to a second aspect of the present invention there is provided a downhole centraliser comprising a S 5 casing, liner or screen centraliser or a production tubing centraliser, the downhole centraliser being adapted to be IND received on a downhole tubular, in use, so as to be a 00 clearance fit around the downhole tubular such that the

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IND downhole centraliser is rotationally and longitudinally 1 0 moveable relative to the downhole tubular, the downhole Scentraliser being a rigid tubular body, the tubular body having at least one first portion and at least one second portion, the at least one first portion and the at least one second portion being statically retained relative to one another, the at least one first portion comprising at least a portion of an outermost surface of the tubular body, the at least one first portion being substantially formed from a first material, and the at least one second portion comprising at least a portion of an innermost surface of the tubular body, the at least one second portion being substantially formed from a second material, the first material having a lower Youngs modulus than the second material, and wherein the first material substantially comprises a thermoplastic polymer.

The at least one first portion may comprise a tubular member providing the outermost surface of the tubular body, the tubular member being substantially formed from the first material, and the at least one second portion comprises a further tubular member extending from or adjacent to one end of the tubular member to or adjacent to another end of the tubular member.

The centralisers of the first and second aspects may be termed "composite" centralisers. These centralisers are therefore "non-unitary" in construction, that is to say, P11611AU ND they are not formed in one piece from one material. They do however, offer a centraliser in which parts made from the first and second materials are static relative to one another, in use. In other words, the centralisers are 5 effectively "one-piece" The Applicant has termed the centraliser of the ND present invention the "EZEE-GLIDER" (Trade Mark).

00 The or each first portion may be circumferentially

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IND integrally continuous, that is, formed in one piece.

The or each first portion may be circumferentially Sintegrally continuous, that is, formed in one piece.

Beneficially the centraliser may be a casing, liner or screen centraliser. However, it will be appreciated that the centraliser may be a production tubing centraliser.

In the first aspect, having a second material with a higher Youngs modulus and, therefore, increased stiffness and strength, e.g. at one or both ends of the centraliser, provides extra stability and strength to stop an end deforming when it strikes ledges, rings or collars during insertion or removal from a well.

In the second aspect the second material contacting the smooth surface of the tubular being centralised can be advantageously made of a low friction material while the outermost surface can be made more of a rugged first material able to withstand collisions with an abrasive rugous borehole wall.

The first material may have a Youngs modulus of 550,000 to 1,000,000 psi (3,793 MPa to 6,896 MPa), and the second material may have a Youngs modulus of 10,000,000 psi (68,960 MPa) or higher. Preferably the first material provides one or more of the following material characteristics as tested by ASTM (American Society for Testing and Materials): P11611AU Youngs Modulus 550,000 psi or 600,000 psi (3,793 MPa or 4,138MPa) or higher (ASTM Test Ref D638) Tensile strength 10,000 psi (690 MPa) or higher (ASTM Test Ref D638) Friction Factor 0.35 or lower (co-efficient of Friction) ASTM Test Dry (thrust washer) against steel Izod input test (notched) 1.6 ft/lbin preferably 3.2 ft/lbin (171 j/m) or higher (ASTM Test Ref D256) HDT (Heat Deflection greater than 185 0 C (ASTM or Distortion Temperature) Test Ref D648 at 66 psi (0.45 MPa)) Chemical resistance Able to withstand chemical attack from most common reagents found in a drilling environment, e.g.

hydrocarbons, brines, weak alkalis and weak acids Specific gravity 1.28 In one implementation the first material may be a polyphthalamide (PPA), e.g. a glass-reinforced heat stablilised PPA such as AMODEL, e.g. AMODEL-AT-1116 HS resin available from BP Amoco,(see http:/www.bpamocoengpolymers.com).

In another implementation the first material may be a polymer of carbon monoxide and alpha-olefins, such as ethylene.

Advantageously, the first material may be an aliphatic polyketone made from co-polymerisation of ethylene and carbon monoxide optionally with propylene.

Advantageously, the first material may be CARILON (Trade Mark) available from Shell Chemicals. CARILON P11611AU \D (Trade Mark) is a class of semi-crystalline thermoplastic materials with an alternating olefin carbon monoxide structure.

In a further implementation the first material may be a nylon resin. Advantageously the first material may be an ionomer modified nylon 66 resin. The first material IND may be a nylon 12 resin, e.g. RILSAN (Trade Mark) 00 available from Elf Atochem.

ND In a yet further alternative implementation the first material may be a modified polyamide (PA).

SThe first material may be a nylon compound such as DEVLON (Trade Mark) available from Devlon Engineering Ltd.

The first material may be of the polyetheretherketone family, EG PEEK (Trade Mark) available from Victrex PLC.

The first material may be ZYTEL (Trade Mark) available from Du Pont. ZYTEL (Trade Mark) is a class of nylon resins which, includes unmodified nylon homopolymers PA 66 and PA 612) and copolymers PA 66/6 and PA 6T/MPMDT etc) plus modified grades produced by the addition of heat stabilizers, lubricants, ultraviolet screens, nucleating agents, tougheners, reinforcements etc. The majority of resins have molecular weights suited for injection moulding, roto-moulding and some are used in extrusion.

Alternatively the first material may be VESCONITE (Trade Mark) available from Vesco Plastics Australia Pty Ltd.

Alternatively the first material may be polytetrafluoroethylene (PTFE).

In such case the first material may be TEFLON (Trade Mark) or a similar type material. TEFLON (Trade Mark) filled grades of PEEL CARILON (Trade Mark) may be used.

These materials are suitable for roto-moulding which is a favoured method of manufacture for economic reasons for P11611AU IND larger component sizes, e.g. greater than 9 5/8" (245 mm) Alternatively, the first material may be PA66, FG30, PTFE from ALBIS Chemicals.

The outermost surface of said body may provide or 5 comprise a plurality of raised portions.

The raised portions may be in the form of IND longitudinally extending blades or ribs or may 00 alternatively be in the form of an array of nipples or

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IND lobes.

Adjacent raised portions may define a flow path therebetween such that fluid flow paths are defined between first and second ends of the tubular body.

Where the raised portions comprise longitudinal blades, such blades may be formed, at least in part, substantially parallel to an axis of the tubular body.

Alternatively, the blades may be formed in a longitudinal spiral/helical path on the tubular body.

Advantageously adjacent blades may at least partly longitudinally overlap upon the tubular body.

Preferably adjacent blades may be located such that one end of a blade at one end of the tubular body is at substantially the same circumferential position as an end of an adjacent blade at another end of the tubular body.

More preferably, the blades may have an upper spiral portion, a middle substantially straight portion and a lower tapered portion.

Advantageously the second material may be a metallic material.

Preferably, the second material may be a bronze alloy such as phosphur bronze or lead bronze, or alternatively, zinc or a zinc alloy.

In a preferred embodiment the second material is lead bronze. Bronze is advantageously selected as it has a high Youngs Modulus (16,675,000 psi (115,000 MPa)) P11611AU O compared to CARILON (around 900,000 psi (6207 MPa), ZYTEL (around 600,000 psi) and AMODEL (870,000 psi (6,000 MPa)) while having friction properties which are better than steel.

S 5 Preferably, in the first aspect at least a portion of an innermost surface of the tubular body may be formed O from the second material.

00 Advantageously, the innermost surface is formed from

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O the second material.

This arrangement provides an inner core with good Sstrength, low friction properties and shock loading.

Preferably, in the second aspect a portion of or adjacent to first and/or second ends of the tubular body may be formed from the second material.

The second material may be arranged in an annulus of a body of the first material.

More preferably there are two annular bodies of the second material each located at respective ends of the body of the first material.

Additionally, the centraliser may include a reinforcing means such as a cage, mesh, bars, rings and/or the like. The reinforcing means may be made from the second material.

At least part of the centraliser according to the first or second aspects of the present invention may be formed from a casting process.

Alternatively or additionally, at least part of the centraliser according to the first or second aspects of the present invention may be formed from an injection moulding process.

Advantageously, at least part of the centraliser according to the first or second aspects of the present invention may be formed from an injection moulding or roto-moulding process.

P1611AU IND Advantageously, also a body of the second material may be retained relative to a body of the first material by an interference fit.

It will be appreciated that the polymeric materials 5 mentioned above may include filler materials, as is known in the polymer art.

O The first material may be around a factor of four 00 times lighter than the second material in air, but may be

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IND around a factor of ten times lighter than the second material in water.

SAccording to a third aspect of the present invention there is provided a centralising apparatus for use in a well-bore, the centralising apparatus including a tubular section and at least one downhole centraliser located thereupon, wherein the centraliser comprises at least one downhole centraliser according to either of the first or second aspects of the present invention.

In a first preferred embodiment the tubular section may be a well-bore casing or liner.

In a second embodiment the tubular section may be a length of production tubing.

In a third embodiment the tubular section may be a screen.

The at least one centraliser may be located so as to surround the tubular section, i.e. the tubular section may be located within the at least one centraliser.

The at least one centraliser may be located longitudinally relative to the tubular section by means of a collar.

The at least one centraliser may be located relative to the tubular section, and may be rotatable relative to the tubular section around a longitudinal axis thereof.

According to a fourth aspect of the present invention there is provided a method of fixing a casing or liner P11611AU IND into a well-bore, the method comprising the steps of: providing a well casing/liner; providing at least one downhole centraliser according to either of the first or second aspects of the present invention; locating the at least one centraliser on the IND casing/liner at a desired position so as to provide a 00 centralising apparatus;

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IND placing the centralising apparatus within the wellbore; and Spumping cement slurry or the like into an annular space between an exterior of the casing/liner and the well-bore.

According to a fifth aspect of the present invention there is provided a method of completing a well, the method comprising the steps of: providing a length of production tubing; providing at least one centraliser according to either of the first or second aspects of the present invention; locating the at least one centraliser on the production tubing at a desired position so as to provide a centralising apparatus; placing the centralising apparatus within a cased or lined well-bore.

Preferably the method comprises the further step of: securing a bottom of a length of the production tubing with a packer to seal the tubing to a casing/liner.

According to a sixth aspect of the present invention there is provided a method of gravel packing a well, the method including the steps of: providing a screen; providing at least one downhole centraliser according to either of the first or second aspects of the present P11611AU invention; locating the at least one downhole centraliser on the screen to provide a centralising apparatus; placing the centralising apparatus within a borehole or perforated casing.

Preferably the method comprises the further step of: placing sand into an annular space between an exterior of the screen and the well-bore or perforated casing.

BRIEF DESCRIPTION OF DRAWINGS A number of embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings which are: Figure 1 Figure 2 Figure 3 a cross-sectional view of a prior art centralising apparatus within a well-bore; a cross-sectional view of a centralising apparatus according to a first embodiment of the present invention; a perspective view from one side and above of a centraliser according to a second embodiment of the present invention; a perspective view from one side and above of a centraliser according to a third embodiment of the present invention; a side view of a centraliser according to a fourth embodiment of the present invention; cross-sectional views of the Figure 4 Figure 5 Figures 6(a) and (b) P11611AU Figures 7 (h)

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00

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Figures 8(a) (d) Figure 9 Figure 10 centraliser of Figure 5 along section lines A A and B B, respectively; examples of outermost surfaces of centralisers according to modifications of embodiments of the present invention; cross-sectional views of various modifications to the centraliser of Figure 5 taken through section line B B; a perspective view from one side and above of a centraliser according to a fifth embodiment of the present invention; a perspective view from one side and above of a centralising apparatus according to a sixth embodiment of the present invention; a perspective view of a centralising apparatus positioned within a well-bore for cementing a well according to a seventh embodiment of the present invention; a perspective view of a centralising apparatus positioned within a casing/liner for completing a well according to an eighth embodiment of the present invention; perspective views of a centralising apparatus Figure 11 Figure 12 Figures 13(a) and (b) P11611AU Figures 14(a) and (b) positioned within a borehole and within a perforated casing respectively, for gravel packing a well according to ninth and tenth embodiments of the present invention; side and end cross-sectional views of a centralising apparatus according to an eleventh embodiment of the present invention; side and end cross-sectional views of a centralising apparatus according to a twelfth embodiment of the present invention; and side and end cross-sectional views of a centralising apparatus according to a thirteenth embodiment of the present invention.

Figures 15(a) and (b) Figures 16(a) and (b) DETAILED DESCRIPTION OF DRAWINGS Reference is initially made to Figure 1 of the drawings which depicts a centralising apparatus, generally indicated by reference numeral 140 as an example of the prior art. Centralising apparatus 140 is located within borehole 152. Centralising apparatus 140 comprises tubular 150 and centraliser 110. The tubular 150 includes a stop collar 144. Centraliser 110 is made of a unitary construction, i.e. of a single piece of polymeric material comprising a plastic material. Demonstrated in Figure 1 is an example of what may occur when the centraliser 110 strikes a ledge or other obstruction when being run.

PI1611AU \D Outermost surface 112 of centraliser 110 sticks at a contact point. The tubular 150 is driven against the centraliser end 118 which will ride over the stop collar -144. Rounded edges on the end 118 can exacerbate the S 5 problem. Nose 146 of the centraliser 110 deforms as the plastic material is forced over the stop collar 144. As IND a result both centraliser 110 and tubular 150 become stuck 00 in the bore hole. Time and costs arise in withdrawing the

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ND tubular 150 and replacing the centraliser 110.

Figure 2 shows a first embodiment of the present Sinvention which addresses one or more of the disadvantages of the prior art. Centralising apparatus 240 comprises a tubular 250 with stop collar 244 and centraliser 210.

Centralising apparatus 240 is located within borehole 252.

The centraliser 210 comprises a tubular body 214, a portion of an outermost surface 212 is formed from a first material and a portion of at least one end 218 is formed from a second material, i.e. insert band 219. The first material has a lower Youngs modulus than the second material. The centraliser 210 is a "composite centraliser", termed "EZEE-GLIDER" (Trade Mark) by the Applicant. A detailed description of the centraliser 210 is provided hereinafter.

As the second material has a higher Youngs modulus than the first material, the centraliser 210 has an increased stiffness and strength at end 218. Thus centraliser 210 has a body 214 which provides an innermost surface 222 and an outermost surface 212. Advantageously the increased strength at the end 218 helps to prevent the nose 246 deforming if it strikes or is struck by a stop collar 244.

Referring now to Figure 3, there is shown a second embodiment of a centraliser for a tubular a casing, liner, screen or even production tubing, or the like), P11611AU \D generally designated 10, according to the present invention. At least a portion of an outermost surface 12 of the centraliser 10 is selected from a first material advantageously providing a good tribological performance S 5 and comprising a thermoplastic polymer, particularly a polymer of carbon monoxide and alpha-olefins, and more ND particularly CARILON (Trade Mark) available from Shell 00 Chemicals, as will hereinafter be discussed in greater

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ND detail. In an alternative, and preferred form of this embodiment, the first material is a polyphthalamide (PPA), such as AMODEL available from BP Amoco. AMODEL is a semicrysallilne polymer offering good mechanical properties over a broad temperature range. AMODEL exhibits a high Heat Deflection Temperature (HTD), high flexural modulus and high tensile strength, as well as good creep resistance and low moisture absorption. In a further form of this embodiment the material is polytetrafluoroeth(yl)ene (PTFE), and particularly TEFLON (Trade Mark).

The centraliser 10 comprises a tubular body 14. The tubular body 14 has a bore 16 extending longitudinally therethrough. The body 14 is provided with outermost surface 12 and ends 18 to 20. Each end 18, 20 is formed from a selected second material, e.g. a metallic material.

In one implementation of this second embodiment, the ends 18, 20 are made of phosphur bronze. In an alternative implementation the ends 18, 20 are made of lead bronze.

This selection of materials ensures that the ends 18, or "nose" of the centraliser 10 has a higher Youngs modulus than that of the body 16, and has friction properties better than steel. The Youngs modulus of CARILON/ZYTEL/AMODEL (Trade Marks) is around 900,000 psi (6,207 Mpa) compared to 16,675,000 psi (115,000 Mpa) for bronze. Thus in bronze, a stress of circa 20 times that P11611AU IND required to deform a plastic end 18, 20 is required. To deform either end 18, 20 over a stop collar strain) requires 4 tonnes for CARILON/ZYTEL/AMODEL (Trade Marks), but 88 tonnes bronze. In use, the likely loading S 5 is likely in the 10 to 20 tonnes range.

Reference is now made to Figure 4 of the drawings 0 which depicts a centraliser 10a, having ends 18a, 20a and 00 an innermost surface 22a and outermost surface 12a. In ND this third embodiment the outermost surface 12a comprises a first material, which is a thermoplastic polymer, 0 particularly a polymer of carbon monoxide and alphaolefins and more particularly CARILON (Trade Mark) available from Shell Chemicals, as will hereinafter be discussed in greater detail. In an alternative, and preferred form of this embodiment, the first material is polyphthalmide (PPA) such as AMODEL available from BP Amoco. In a yet further form of this embodiment the material is polytetrafluoroeth(yl)ene (PTFE), and particularly TEFLON. Ends 18a, 20a and the innermost surface 22a are constructed from lead bronze. This composite centraliser 10a has the advantages of a rigid inner body providing an improved journal bearing and also ends for good thrust load bearing.

CARILON (Trade Mark) is a semi-crystalline aliphatic polyketone as disclosed in Shell Chemical Literature available from their web-site http://www.shellchemical.com as at 10 November, 1998 and included herein by reference.

According to the literature CARILON (Trade Mark) is characterised by the following: X Short moulding cycles and good mould definition X Low warpage and no need for post-moulding conditioning X Superior resilience and snapability X Very good impact performance over a broad temperature P11611AU \D range 0 X Very good chemical resistance and barrier performance X Very good hydrolytic stability X Good friction/wear characteristics and low noise generation A range of CARILON (Trade Mark) is used depending on the

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00 performance required and the fabrication method, i.e.

9\ extrusion or injection moulding. The current range is:

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Cq X SC:2544-97 CARILON7 D26CX100 Advanced extrusion grade CI X SC;2545-97 CARILON7 D26FX100 General purpose extrusion grade X SC:2546-97 CARILON7 D26HM100 General purpose injection moulding grade X SC:2547-97 CARILON7 D26VM100 High-flow injection moulding grade X SC:2548-97 CARILON7 DB6G3A10 15% Glass reinforced general-purpose injection moulding grade X SC:2549-97 CARILON7 DB6GA10 30% Glass reinforced general-purpose injection moulding grade X SC;2550-97 CARILON7 DB6FOA10 Flame retarded (Vinjection moulding grade X SC:2551-97 CARILON7 DB6F5G40 Flame retarded (V- 20% glass reinforced, injection moulding grade X SC:2552-97 CARILON7 DB6F1G40 Flame retarded (V-l) tracking resistance 15% glass reinforced injection moulding grade X SC:2533-97 CARILON7 DA6L1A10 Lubricated injection moulding grade X SC:2554-97 CARILON7 DA6P2L10 High performance lubricated injection moulding grade X SC:2557-97 CARILON7 DB6G6P30 Lubricated glass reinforced injection moulding grade.

P11611AU \D For some environments ZYTEL (Trade Mark) can be used.

p ZYTEL (Trade Mark) is a nylon resin available from Du Pont which can be injection moulded, and is disclosed on their web-site http://www.dupont.com as at 12th November 1998, 5 included herein by reference. Currently thirteen grades of ZYTEL (Trade Mark) can be used, namely: ND X 408L NCO Ionomer modified nylon 66 resin 00 SX 450HSL BK 152 Olefinic/rubber modified nylon 66 D resin X 3189 NCO10 Cube blend, stiff, rubber C- modified nylon 66 resin X FN718 010 Flexible grafted ionomer modified nylon 66 resin X FN714 NC010 Very flexible grafted ionomer modified nylon 66 resin X CFE4003HS BK245 Heat stabilized toughened black nylon 66 resin X CFE4004HS NC010 Heat stabilised toughened nylon 66 resin X CFE4005HS BK246 Heat stabilized highly toughened black nylon 66 resin X CFE4006HS NC010 Heat stabilized highly toughened nylon 66 resin which are toughened nylons X ST801 NC010 Grafted rubber modified nylon 66 resin X ST801W NC010 Grafted rubber modified nylon 66 resin X ST901L NC095 Grafted rubber modified nylon 66 resin X ST901L NC010 Grafted rubber modified amorphous nylon resin which are super tough nylons.

P11611AU \D A further alternative plastic material which can be used in VESCONITE (Trade Mark). It is available from Vesco Plastics Australia Pty Ltd. VESCONITE (Trade Mark) exhibits greater hardiness, lower friction, negligible water absorption and higher chemical resistance than nylon. VESCONITE (Trade Mark) can be machined. Of better IND quality is VESCONITE HILUBE (Trade Mark) which can be 00 injection moulded.

IND Referring now to Figures 5, 6(a) and 6(b) there is illustrated a centraliser 10b according to a fourth Sembodiment of the present invention. The centraliser is of composite construction with ends 18b, 20b and innermost surface 22b, as shown in Figures 6(a) and 6(b), comprising of a lead bronze body 100b bonded to a tough abrasion resistant material body 105b, in this embodiment CARILON (Trade Mark) or AMODEL (Trade Mark), providing outermost surface 12b. The outermost surface 12b of the body 105b includes a number of raised portions in the form of longitudinally extended blades 24 or ribs. Adjacent blades 24 define a flow path between the ends 18b, 20b of the body 14b. The blades 24 are parallel to an axis of the tubular body 14b.

Figures show a variety of outermost surfaces 12c-j which can be made in a plastics material, by way of example. Ends and innermost surfaces have been omitted from these figures to aid clarity. Figures 7(b) and 7(c) illustrate arrays of nipples 26d or lobes 28e as the raised portions.

Figures show an outermost surface of raised portions in the form of blades 24c,f-j wherein adjacent blades partly longitudinally overlap on the tubular body 14c-j. For some embodiments e.g. Figures 7(g) and 7(h) adjacent blades are located such that one end of a blade 25c,h-j at one end 18c,h-j of the P11611AU IND tubular body 14c,h-j is at the same longitudinal position as an end 27c,h-j of an adjacent blade at another end of the tubular body 14c,h-j. Figures 7(d) and 7(e) illustrate blades 24f,g having an upper spiral section 25f,g a middle substantially straight section 23f,g and a lower tapered section 27f,g. In these ID embodiments the outermost surfaces 12c-j may be moulded, 00 e.g. injection moulded, at surface 14c-j, onto a metallic

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ND tubular body (not shown).

Reference is now made to Figures which show Sa series of, modified embodiments, each shown through section B-B of Figure 5, of modifications to the centraliser 10b according to the present invention. These Figures illustrate, by way of example only, possible arrangements of the two materials which make up the centraliser Figure 8(a) shows ends 18k, 20k having portions of a second material, preferably leaded bronze, bonded or otherwise fixed by an interference fit) to a tubular body 14k by a snap ring type arrangement. Innermost surface 22k and outermost surface 12k surfaces are formed from the first material, preferably CARILON (Trade Mark) or AMODEL (Trade Mark), as described hereinbefore.

In Figure ends 181, 201 have smaller bonded sections of leaded bronze arranged as a ring around the tubular body 141. Figures 8(c) and 8(d) illustrate embodiments where the second material is a ring sited at each end, but away from annular faces 25m,n, 27m,n of the ends. In these embodiments part of the innermost surface, part of the outermost surface and/or part of end surfaces are all made of the first material, e.g. CARILON (Trade Mark) or AMODEL (Trade Mark). The second material, leaded bronze, formed in an integral ring or annulus provides stability and rigidity to the centraliser P11611AU ND The centraliser 10b may be formed from an injection moulding process. Alternatively, the centraliser 10b may be formed from a casting process. Advantageously, the centraliser 10b is formed from a roto-moulding process.

S 5 Those of skill in the art will appreciate the appropriate process for each embodiment shown. For some embodiments ND e.g. Figures 5 to the second material may be cast 00 while the first material is injection moulded as a plastic

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IND coating over a metallic body. Thus the second material may be "bonded" to the first.

Reference is now made to Figure 9 of the drawings which depicts a centraliser, generally indicated by reference numeral 10w, according to a fifth embodiment of the present invention. Centraliser 10w includes a tubular body 14w, which is of a second material, preferably a metallic material. A portion 24w of the outermost surface 12w of the centraliser 10w is of a first plastics material. The first material has a lower Youngs modulus than the second material. The portion of the outermost surface 12w comprises a series of longitudinally extending blades 24w. The blades 24w may be modified to have a shape, position and orientation as shown in Figures When assembled, the blades 24w are attached to outermost surface 12w of the body 14w, e.g. by bonding, bolting, screwing or the like, at connection points 31w.

Referring now to Figure 10 there is illustrated centralising apparatus, generally indicated by reference numeral 40p, according to a sixth embodiment of the present invention. The apparatus 40p comprises a tubular section 42p onto which is mounted at least one centraliser as described hereinbefore. The centraliser includes an outermost surface 12p as described hereinbefore with reference to Figures 7(d) and The outermost surface is made of a first material comprising P11611AU IO CARILON (Trade Mark) or AMODEL (Trade Mark). Ends 18p, are formed from a second material, preferably leaded bronze such that the first material has a lower Youngs modulus than the second material. The innermost surface S 5 (not shown) may be made of the first material or beneficially of the second material. The tubular section IO 42p may be a casing, liner, production tubing or screen.

00 The centraliser 10p may be rotatable relative to the

NO

ND tubular section 42p along a longitudinal axis thereof.

S 10 Additionally illustrated in Figure 10 is a stop collar S44p. Stop collars 44p may be positioned on the tubular section 42p at either end of the centraliser During the running of the tubular section 42p the outermost surface 12p of the centraliser 10p may contact ledges, possibly the ledges within the BOP stack cavities and wellhead when run in a cased hole, or to ledges and rugous boreholes when run in an open hole. The effect of the centralisers end 18p being subjected to such forces is to drive the centraliser 10p along the tubular 42p in the opposite axial direction to that of the tubular motion.

Thus "nose" 46p of the centraliser 10p is driven into the stop ring or casing collar 44p. When the tubular 42p is rotated (a common procedure when running tubular downhole, converting drag friction into torque friction) the centraliser nose 46p will be forced against the stop collar 44p and the tubular 42p then rotated thus causing the centraliser nose 46p to act as thrust bearing.

If the nose 46p is made of a material that is a thermoplastic material, an aluminium material or some lower Youngs Modulus material, the centraliser 10p may ride over the collar 44p, thus being stretched, so creating the possibility of jamming the centraliser against the borehole wall. In the present invention the nose 46p of the centraliser 40p is of a material with a P11611AU \D higher Youngs modulus than that of the body material, yet has friction properties better than steel. For the preferred embodiment, the body material is CARILON (Trade Mark) or AMODEL (Trade Mark) where the Youngs modulus of S 5 CARILON/ZYTEL/AMODEL (Trade Marks) is around 900,000 psi (6,207 MPa) and AMODEL is 870,000 psi (6,000 MPa) and the IND "nose" or end material is leaded bronze where the Youngs 00 modulus is 16,675,000 psi (115,000 MPa). In bronze, a

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IND stress of circa 20 times that required to deform the plastic nose is required. To deform the nose 46p over the Stop collar 44p strain) requires 4 tonnes CARILON, 88 tonnes bronze. In use, the likely loading is in the to 20 tonnes range.

Referring to Figure 11, there is illustrated a seventh embodiment of a centralising apparatus 40q similar to the centralising apparatus 40p of Figure 10. In Figure 11 where the tubular section of 42q of the centralising apparatus 40q is a casing or liner 50q, in use, the apparatus 40q is located within a well bore 52q such that the innermost surface 22q of the at least one centraliser is a clearance fit rotatable around the casing or liner 50q while the outermost surface 12q contacts the borehole walls.

In use, the centraliser 10q may aid cementing of a well. The casing or liner 50q is cemented into the well bore 52q, by the following method steps of: providing a well casing/liner providing the at least one centraliser locating the least one centraliser 10q on the casing/liner 50q at a desired position so as to provide a centralising apparatus placing the centralising apparatus 40q within the well bore 52q; and pumping cement slurry 70q into an annular space 72q P11611AU IN between an exterior of the casing/liner 50q and the well bore 52q.

Referring now to Figure 12, where the tubular section 42r of the centralising apparatus 40r is a length of a S 5 production tubing 54r, in use, the apparatus 40r is located within a casing or liner 56r located in a borehole IN 58r such that the innermost surface 22r of the centraliser 00 is a clearance fit rotatable around the production

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IN tubing 54r while the outermost surface 12r contacts the 10 innermost surface 60r of the casing or liner 56r.

SIn use, the centraliser lOr may aid completion of a well. This method of completing a well comprises the steps of: providing a length of the production tubing 54r; providing the at least one centraliser locating the at least one centraliser 10r on the production tubing lOr at a desired position so as to provide centralising apparatus placing the centralising apparatus 40r within a cased or lined well bore 58r; and securing a bottom 74r of the length of production tubing 54r with a packer 76r to seal the tubing 54r to the casing/liner 56r.

Referring now to Figure 13(a), where the tubular section 42s of the centralising apparatus 40s is a screen 62s, the screen 62s being a section of production tubing including slots or holes, the apparatus 40s is located within the open hole end of a borehole 64s. The outermost surface 12s of the centraliser 10s will contact the borehole wall 66s while the innermost surface 22s of the centraliser 10s is a clearance fit rotatable around the screen 62s.

Alternatively, as shown in Figure 13(b), apparatus may be located at a section of perforated casing 66t P11611AU \D within borehole 64t wherein the centraliser 10t is then located between the outer surface of the screen 68t and the perforated casing 66t.

In use the centralisers 10s, 10t may aid in the S 5 gravel packing of a screen 62s,68t in a well. This method of gravel packing a well includes the steps of: \D providing screen 62s, 68t; 00 providing the at least one centraliser 10s,10t;

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ND locating the at least one centraliser 10s,10t on the S 10 screen 62s,68t to provide centralising apparatus 40s,40t; Splacing the centralising apparatus 40s,40t within a borehole 64s or perforated casing 66t; and placing sand 78s,78t into an annular space between an exterior of the screen 62s,68t and the well bore 64s or perforated casing 68t.

It will be appreciated that a principle advantage of the present invention is to provide a centraliser for centralising a downhole tubular which has the combined advantages of a rigid construction to prevent deformation of the centraliser when thrust against collars or stops, while providing a centraliser with a low friction outer surface for ease of installation within, e.g. a bore-hole or casing.

It will be appreciated by those skilled in the art that the embodiments of the invention hereinbefore described are given by way of example only, and are not meant to limit the scope of the invention in any way. It is noted that the term "centraliser" has been used herein; however it will be appreciated that the device also acts as a "glider". In addition though the disclosed embodiments illustrate symmetrical centralisers, it will be appreciated that the second material may be provided only at a single end of the centraliser.

Further, it will be appreciated that a benefit of the P11611AU IND embodiments hereinbefore disclosed is the provision of electrical isolation between the tubular body centralised by the centraliser, and any object or surface which the outerside of the centraliser touches or otherwise rests S 5 against. In such case the invention does not need provision of blades etc, and the invention comprises a ND downhole tool in the form of an electrical 00 isolator/sheath/sleeve, e.g. 25 to 30 ft (7.7 to 9.3 m) in

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IND length.

The reference in this specification to any prior Spublication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

P11611AU

Claims

1. A downhole centraliser comprising a casing, liner or screen centraliser or a production tubing centraliser, the downhole centraliser being adapted to be received on a downhole tubular, in use, so as to be a clearance fit ND around the downhole tubular such that the downhole 00 centraliser is rotationally and longitudinally moveable \O ND relative to the downhole tubular, the downhole centraliser being a rigid tubular body, the tubular body O having a first portion and at least one second portion, the first portion and the at least one second portion being statically retained relative to one another, the first portion comprising a tubular member providing an outermost surface of the tubular body, the first portion being substantially formed from a first material, and the at least one second portion comprising a ring member provided at or adjacent to one end of the tubular member, the at least one second portion being substantially formed from a second material, the first material having a lower Youngs modulus than the second material, and wherein the first material substantially comprises a thermoplastic polymer.

2. A downhole centraliser as claimed in claim 1, wherein the at least one second portion comprises a further ring member provided at or adjacent to another end of the tubular member.

3. A downhole centraliser as claimed in either of claims 1 or 2, wherein at least a portion of an innermost surface of the tubular body is provided by the ring member and optional further ring member. P11611AU ND 4. A downhole centraliser comprising a casing, liner or screen centraliser or a production tubing centraliser, the downhole centraliser being adapted to be received on a downhole tubular, in use, so as to be a clearance fit around the downhole tubular such that the downhole centraliser is rotationally and longitudinally moveable ID relative to the downhole tubular, the downhole 00 centraliser being a rigid tubular body, the tubular body \O IND having at least one first portion and at least one second 1 0 portion, the at least one first portion and the at least Sone second portion being statically retained relative to one another, the at least one first portion comprising at least a portion of an outermost surface of the tubular body, the at least one first portion being substantially formed from a first material, and the at least one second portion comprising at least a portion of an innermost surface of the tubular body, the at least one second portion being substantially formed from a second material, the first material having a lower Youngs modulus than the second material, and wherein the first material substantially comprises a thermoplastic polymer. A downhole centraliser as claimed in claim 4, wherein the at least one first portion comprises a tubular member providing the outermost surface of the tubular body, the tubular member being substantially formed from the first material, and the at least one second portion comprises a further tubular member extending from or adjacent to one end of the tubular member to or adjacent to another end of the tubular member. P11611AU \O 6. A downhole centraliser as claimed in any of claims 1 to 5, wherein the or each first portion is circumferentially formed in one piece.

7. A downhole centraliser as claimed in any of claims 1 to 6, wherein the or each second portion is NO circumferentially formed in one piece. 00 DO 8. A downhole centraliser as claimed in any of claims 1 to 7, wherein the centraliser is a casing, liner or Sscreen centraliser.

9. A downhole centraliser as claimed in any of claims 1 to 7, wherein the centraliser is a production tubing centraliser. A downhole centraliser as claimed in any of claims 1 to 9, wherein the first material has a Young's modulus of 550,000 to 1,000,000 psi (3,793 to 6,896 MPa), and the second material has a Youngs modulus of 10,000,000 psi (68,960 MPa) or higher.

11. A downhole centraliser as claimed in any of claims 1 to 10, wherein the first material is a polyphthalamide (PPA) optionally having glass reinforcement.

12. A downhole centraliser as claimed in any of claims 1 to 10, wherein the first material is a polymer of carbon monoxide and alpha-olefins.

13. A downhole centraliser as claimed in any of claims 1 to 10, wherein the first material is an aliphatic polyketone made from co-polymerisation of ethylene and carbon monoxide optionally with propylene. P11611AU O 14. A downhole centraliser as claimed in any of claims 1 to 10, wherein the first material is a semi-crystalline thermoplastic material with an alternating olefin carbon monoxide structure. ND 15. A downhole centraliser as claimed in any of claims 1 00 to 10, wherein the first material is a nylon material. \O \O IN

16. A downhole centraliser as claimed in any of claims 1 0 to 10, wherein the first material is a polyamide (PA).

17. A downhole centraliser as claimed in any of claims 1 to 10, wherein the first material is polyetheretherketone.

18. A downhole centraliser as claimed in any of claims 1 to 10, wherein the first material is polytetrafluoroethylene (PTFE).

19. A downhole centraliser as claimed in any preceding claim, wherein the outermost surface of said tubular body provides or comprises a plurality of raised portions.

20. A downhole centraliser as claimed in claim 19, wherein the raised portions are in the form of longitudinally extending blades or ribs or an array of nipples or lobes.

21. A downhole centraliser as claimed in either of claims 19 or 20, wherein adjacent raised portions define a flow path therebetween such that fluid flow paths are defined between first and second ends of the tubular body. P11611AU I I 34 \D 22. A downhole centraliser as claimed in either of claims 20 or 21, wherein where the raised portions comprise longitudinal blades, the blades being formed, at -least in part, substantially parallel to a longitudinal axis of the tubular body. ND 23. A downhole centraliser as claimed in either of 00 e- claims 20 or 21, wherein the blades are formed in a ND longitudinal spiral or helical path on the tubular body.

24. A downhole centraliser as claimed in claim 23, wherein adjacent blades at least partly longitudinally overlap upon the tubular body.

25. A downhole centraliser as claimed in claim 24, wherein adjacent blades are located such that one end of a blade at one end of the tubular body is at substantially the same circumferential position as an end of an adjacent blade at another end of the tubular body.

26. A downhole centraliser as claimed in any of claims to 22, wherein the blades have an upper spiral portion, a middle substantially straight portion and a lower tapered portion.

27. A downhole centraliser as claimed in any preceding claim, wherein the second material is a metallic material.

28. A downhole centraliser as claimed in any preceding claim, wherein the second material is a bronze alloy, such as phosphor bronze or lead bronze, or alternatively zinc or a zinc alloy. P11611AU \D 29. A downhole centraliser as claimed in any preceding claim, wherein the downhole centraliser includes a reinforcing means such as a cage, mesh, bars, and/or rings. A downhole centraliser as claimed in claim 29, IND wherein the reinforcing means are made of the second 00 material. (N

31. A downhole centraliser as claimed in any preceding 0 claim, wherein at least part of the downhole centraliser is formed from a casting process.

32. A downhole centraliser as claimed in claim 33, wherein at least part of the downhole centraliser is formed from an injection moulding or roto-moulding process.

33. A downhole centraliser as claimed in any preceding claim, wherein there is provided one first portion, the at least one second portion being retained relative to the first portion by an interference fit.

34. A downhole centraliser as claimed in any preceding claim, wherein the or the at least one first portion and at least one second portion are static relative to one another. A centralising apparatus for use in a well-bore, the centralising apparatus including a tubular section and at least one downhole centraliser located thereupon, wherein the at least one downhole centraliser comprises a downhole centraliser according to any of claims 1 to 34. P11611AU \D 36. A centralising apparatus as claimed in claim wherein the tubular section is a well-bore casing or liner.

37. A centralising apparatus as claimed in claim wherein the tubular section is a screen. 00

38. A centralising apparatus as claimed in claim 37, IND wherein the tubular section is a length of production tubing.

39. A centralising apparatus as claimed in any of claims to 38, wherein the at least one downhole centraliser is located so as to surround the tubular section, such that the tubular section is located within the at least one downhole centraliser. A centralising apparatus as claimed in any of claims to 39, wherein the at least one downhole centraliser is located longitudinally relative to the tubular section by means of a stop collar.

41. A centralising apparatus as claimed in any of claims to 40, wherein the at least one downhole centraliser is located relative to the tubular section and is rotatable relative to the tubular section around a longitudinal axis thereof.

42. A method of fixing a casing or liner into a well- bore, the method comprising the steps of: providing a well casing or liner; providing at least one downhole centraliser according to any of claims 1 to 34; P11611AU \D locating the at least one downhole centraliser on the casing or liner at a desired position so as to provide a centralising apparatus; placing the centralising apparatus within the well- 5 bore; and pumping cement slurry into an annular space between IND an exterior of the casing or liner and the well-bore. 00 IND 43. A method of gravel packing a well, the method including the steps of: Sproviding a screen; providing at least one downhole centraliser according to any of claims 1 to 34; locating the at least one downhole centraliser on the screen to provide a centralising apparatus; and placing the centralising apparatus within a well- bore or perforated casing.

44. A method as claimed in claim 43, wherein the method comprises the further step of: placing sand into an annular space between an exterior of the screen and the well-bore or perforated casing.

45. A method of completing a well, the method comprising the steps of: providing a length of production tubing; providing at least one downhole centraliser according to any of claims 1 to 34; locating the at least one downhole centraliser on the production tubing at a desired position so as to provide a centralising apparatus; and placing the centralising apparatus within a cased or lined well-bore. P11611AU a t 38 \NO 46. A method as claimed in claim 45, wherein the method comprises the further step of: securing a bottom of a length of the production tubing with a packer to seal the tubing to a casing or liner. IO 47. A downhole centraliser as hereinbefore described 00 with reference to Figure 2, Figure 3, Figure 4, Figures NO IO to Figures 7(a) to Figures 8(a) to Figure 9 or Figure

48. A centralising apparatus as hereinbefore described with reference to Figure 11, Figure 12, Figures 13(a) and Figures 14 and Figures 15(a) and or Figures 16(a) or

49. A method of fixing a casing or liner into a well- bore as hereinbefore described with reference to Figure 11. A method of gravel packing a well as hereinbefore described with reference to Figures 13(a) or

51. A method of completing a well as hereinbefore described with reference to Figure 12. DATED 17 July 2006 Brunel Oilfield Services (UK) Limited By DAVIES COLLISON CAVE Patent Attorneys for the applicant P11611AU